This invention pertains to a tool for venting the cuff area of a separable loadbreak connector to reduce the likelihood of flashover upon separation of the connector""s male/female components
High voltage cables to padmount transformers, reactors, and other underground power distribution apparatus make use of several types of removable connectors referred to as xe2x80x9cseparable insulated connectorsxe2x80x9d. The requirements and constructional dimensions of such connectors are specified in ANSI/IEEE Standard 386, Separable Insulated Connector Systems for Power Distribution Systems Above 600 V. Connectors that can be removed while the apparatus remains energized are referred to as xe2x80x9cloadbreak connectorsxe2x80x9d. The advantage of a load-break connector is that it permits minimizing the number of customers who will be without power while maintenance is in progress by selectively de-energizing individual pieces of apparatus rather than a whole section of line.
FIG. 1 depicts one type of loadbreak connector 10 for electrically conductively coupling cable 12 to apparatus 14. Connector 10 consists of female elbow portion 16, male bushing insert 18 and bushing well 20. As is well known to persons skilled in the art, other types of loadbreak connectors (not shown) may utilize a non-field-replaceable integral bushing instead of a bushing insert; or, a female component such as a parking stand and feedthrough mated to a male elbow; or, an alternative male type cuffed component such as a cap; or, alternative male-female tee connector components. In all cases, the male component has a cuff such as cuff 44 shown in FIG. 1. Elbow portion 16 includes a grounding wire 21, an operating eye 22, and a test point 24 having a removable cap 26. A compression lug 28 within elbow portion 16 is mechanically and electrically conductively coupled between cable 12 and probe 30. Bushing well 20 is mounted on apparatus 14 such that connection pin 32 extends within tapered cavity 34 of bushing well 20. A mating tapered portion 36 of bushing insert 18 having a threaded aperture 38 is fitted within cavity 34, and connection pin 32 is threaded into aperture 38. The opposed tapered portion 40 of bushing insert 18 is fitted within mating tapered aperture 42 in elbow portion 16 and sealed by fitting cuff 44 over shoulder 41 of bushing insert 18, such that probe 30 makes electrical contact with connection pin 32 through aperture 38 and other internal connecting mechanisms (not shown). In operation, internal portions of loadbreak connector 10 including compression lug 28, probe 30, tapered portions 36 and 40, aperture 38 and pin 32 are at high voltage relative to the external housing or shield portions 46, 48 of loadbreak connector 10, which remain at ground potential.
Loadbreak connector 10 is conventionally opened (by a qualified, trained operator) by coupling an insulated tool known as a xe2x80x9chotstickxe2x80x9d (sometimes alternatively called a xe2x80x9chammer stickxe2x80x9d, xe2x80x9cimpact stickxe2x80x9d, lever stickxe2x80x9d, xe2x80x9cuniversal grip-allxe2x80x9d or xe2x80x9cshotgun stickxe2x80x9d), to operating eye 22 then pulling on the hotstick to separate elbow portion 16 from bushing insert 18. As elbow portion 16 begins to move away from bushing insert 18, partial vacua are created inside aperture 42 until elbow portion 16 has moved sufficiently far away from bushing insert 18 to allow such partial vacua to vent to the ambient air. Such partial vacua can be detrimental to the strength of the high voltage insulation in loadbreak connector 10. More particularly, weakening of the insulation, either directly or indirectly attributable to such partial vacua, is thought to be responsible for high voltage flashovers which sometimes occur along the operating interface comprising tapered portion 40 of bushing insert 18 and the mating tapered aperture 42 in elbow portion 16. Besides posing a safety hazard to personnel working with loadbreak connectors, flashovers can cause considerable equipment damage and consequential equipment outage time. It is accordingly desirable to eliminate or minimize these partial vacua so as to eliminate or minimize potential flashovers.
The prior art has addressed the problem of partial vacua and flashovers in a variety of ways. One approach, exemplified by U.S. Pat. No. 5,957,712 Stepniak (believed to be marketed under the trademark Elastimold(trademark) by Thomas and Betts Corporation, Hackettstown, N.J.) has been to provide slots in the shoulder of the bushing insert to vent a cavity formed between the elbow cuff and the transition shoulder portion of the bushing insert with ambient air. According to Stepniak, this avoids a decrease in pressure within the connection region and avoids a decrease in the dielectric strength of the air therein, thus preventing flashover. Alternatively, the elbow portion of Stepniak""s connector includes an insulative layer covering a portion of the probe to increase the distance between the energized electrode and ground; or, an insulative layer is provided within the elbow""s aperture.
Another prior art approach, exemplified by U.S. Pat. No. 5,857,862 Muench et al. has been to provide a semi-conductive insert which includes an additional volume of air which surrounds energized portions of the connector""s elbow or cap. During separation, the semi-conductive insert stretches, increasing the volume of the interior space between the elbow (or cap) and the bushing. According to Muench et al., the additional volume of air lessens the reduction in pressure during separation so that the dielectric strength of the air surrounding energized portions of the elbow (or cap) is maintained at a higher level. The increased dielectric strength of the air is said to significantly reduce the possibility of a flashover occurring during separation of the elbow (or cap) from the bushing.
Yet another prior art approach, exemplified by U.S. Pat. No. 5,846,093 Muench, Jr. et al. has been to line the elbow with an elastic insulator. When the elbow and bushing are connected, a cavity is formed there-between. A rigid member prevents the connector from stretching substantially when the elbow and bushing are disconnected. According to Muench, Jr. et al., because the connector is prevented from stretching, the air pressure in the elbow-bushing cavity remains relatively high during disconnection. The dielectric strength of the air in the cavity, which is a function of pressure, is said to also remain high, so that the possibility of flashover is substantially eliminated.
U.S. Pat. No. 5,655,921 Makal et al. addresses the flashover problem in a variety of ways. In one aspect, exposed conductive portions of the male connector are supplemented with insulated portions such that energized points on the energized connector are placed a greater distance away from the nearest ground plane on the complementary connector. The additional insulation is said to compensate for reductions in dielectric strength of the air occurring during separation of the male connector from the female connector. The bushing""s semi-conductive ground shield (i.e. depicted at 46, 48 in the case of loadbreak connector 10 shown in FIG. 1) is also supplemented by an insulating sleeve, which is said to effectively remove a common ground plane to which an arc might tend during a flashover. In another aspect, a substantial airtight seal is prevented between elastomeric seals of the female connector and the probe of the male connector. The connection being thus vented, the available volume of air surrounding the energized components of the connector assembly is increased. The probe portion of the elbow is configured to prevent substantial sealing between the connector components. An annular reduced diameter recess is located between the probe""s metal rod and its arc follower (i.e. the tip portion of probe 30 shown in FIG. 1) and is elongated to prevent substantially airtight sealing between the elbow and bushing during the initial stages of the loadbreak operation itself. The Makal et al. probe may alternatively be hollow and vented or include a groove disposed along its length. The Muench et al., Muench, Jr. et al. and/or Makal et al. devices are believed to be marketed under the trademarks RTE(trademark) and/or Posi-Break(trademark) by the Cooper Power Systems division of Cooper Industries Inc., Pittsburgh, Pa.
A still further prior art approach, believed to be marketed under the trademark Safe-T-Ring(trademark) by the Chardon Electrical Components division of Hubbell Power Systems, Inc., Greeneville, Tenn., has been to retrofit the loadbreak connector with a ported ring encircling the cuff entry, to prevent vacuum formation within the cuff.
The aforementioned prior art approaches entail structural alteration of the loadbreak connector itself. Implementation of any such approach would require an electric utility operator to replace or retrofit existing elbows and/or bushings. The conversion process could take several years to complete. During conversion, operators would probably experience some flashover incidents, since the connectors must be opened before they can be structurally altered.
As an alternative to structurally altering the loadbreak connector itself, one may modify the apparatus (i.e. padmount transformer, reactor, etc.) to incorporate internal switches allowing the apparatus to be de-energized before the connectors are opened. However, addition of such switches would add significant cost to the apparatus, assuming such switches were added only to newly installed apparatus. Retrofitting in-service apparatus to include such switches would be very costly and could also take years to implement.
Some utility operators have implemented procedures whereby the line is de-energized by pulling the tap-off fuse before opening a connector. However, this defeats the purpose of a loadbreak connector, since all the customers on the tap would be without power while work was in progress. Some operators have also suggested that reheating the connector reduces the probability of a flashover. But, reheating the connector consumes time and may only apply to planned outages where several hours advance notice is given to the operator.
The present invention adopts a different approach, whereby a special tool is used to vent the cuff area between the separable male/female connector components.
The invention provides a separable loadbreak connector cuff venting tool having a handle formed of an electrical insulator material. An electrically insulating head is fixed on the handle""s forward end. The head is sized and shaped for mating engagement with the loadbreak connector""s cuff. A rearwardly directed force applied along the handle""s longitudinal axis gradually slides the head into the cuff, thereby venting any partial vacuum from within the cuff to the surrounding atmosphere and reducing the likelihood of flashover.
Advantageously, a rearwardly projecting member sized and shaped for slidable insertion within the cuff is formed on the head. The member is preferably a wedge. Most preferably, two or more opposed wedges are provided. The wedges are rearwardly tapered and may have rounded rearward tips and/or rearward concave curvature.
Optionally, a clamp may be provided on a rearward portion of the handle for use in clamping the tool""s handle to a hotstick handle. As another option, a pivot fulcrum may be provided on the rearward portion of the tool""s handle for use in pivotally levering the tool""s handle away from the hotstick handle. The tool""s head, clamp and pivot fulcrum extend transversely away from the tool""s handle, in the same direction.